Lizzie loves to stargaze at night. She has noticed that the moon appears to change shape over the course of the month, and she wants to investigate why this happens. She hypothesizes that the relationship of the sun, Earth, and moon creates shadows on the moon. She sets up an experiment with a light bulb to represent the sun, a large beach ball to represent Earth, and a smaller foam ball to represent the moon. She researches the position of the sun, Earth, and moon at different times of a month and makes a model of the entire system.

List at least three variables Lizzie should control during the experiment. For each variable identified, give a specific suggestion for how Lizzie can control it.